Digital Combat Simulator World (DCS World) is a free, unified interface for all DCS products; you can think of DCS World as a simulation operating system. DCS modules that can plug into DCS World can include aircraft, maps, ground units, campaigns, etc. Not only can DCS World include modules developed internally by Eagle Dynamics, but it can also include those by certified third party developers.
DCS World not only includes the Graphical User Interface (GUI) that ties all DCS products together in a single installation, but it also includes the global aspects of the simulation world that pertains to all modules. This includes such items such as the Artificial Intelligence (AI), rendering system, mission editor, effects, AI units, semi-dynamic campaign system, and audio environment.
When a user purchases a DCS module, the module only includes content specific to that module. Thus, it requires DCS World to run.